1. Field of the Invention
The present invention relates to an optical fiber coupler reinforcing member and to an optical fiber coupler.
2. Description of the Related Art
Optical fiber couplers have a coupling section (the optical fiber coupler main body) which connects a plurality of optical fibers and, at the coupling section, separate or combine the light within the optical fibers. In addition, the coupling sections are extremely fine compared with the normal optical fiber and are deformed or break simply due to the application of slight external forces, and there is a risk that the function of the coupling section will be lost. Therefore, generally, in optical fiber couplers, the coupling section is protected by being housed within a reinforcing member.
As this reinforcing member, conventionally, an approximately rectangular-shaped member having a square bracket-shaped recess (longitudinal groove) in cross-section in which the coupling section is housed, as shown in FIG. 8, and an approximately cylindrical-shaped member having a C-shaped recess in cross-section in which the coupling section housed, as shown in FIG. 9, have been used. Here, both FIG. 8 and FIG. 9 show cross-sections of conventional optical fiber couplers, and the coupling sections L of the optical fibers are housed in the recesses provided in reinforcing members A and B respectively. The coupling sections L are fixed in the reinforcing members by means of, for example, adhesive.
In addition, in order to prevent changes in the properties, and the like, due to deterioration, deformation, damage, and distortion resulting from differences in the coefficient of expansion of the optical fiber and the reinforcing member due to temperature change, these reinforcing members comprise, for example, quartz, or hard metals having a coefficient of expansion close to that of the optical fiber such as super invar materials and invar materials or the like, and for the case of a metal member, the surface thereof is subjected to gold plating.
In addition, metal members which form these reinforcing members usually have a surface roughness of less than 1 μm, for example, for super invar materials or invar materials, the surface roughness is 0.4 to 0.7 μm.
However, according to the above-mentioned conventional technology, for the reinforcing member comprising the approximately rectangular member having a square bracket-shaped cross-section (hereinafter referred to as the first conventional technology), when a force F is applied from the outer wall surface W1 toward the wall surface W2 of the recess, that force becomes concentrated on the corner C1 formed by the wall surface W2 and the bottom surface W3 of the recess, and therefore, there is a problem that the section of corner C1 becomes brittle, and the recess of reinforcing member A is damaged (refer to FIG. 8).
On the other hand, for the reinforcing member comprising an approximately cylindrical-shaped member having a C-shaped cross-section (hereinafter referred to as the second conventional technology), since the outer wall surface W4 and the wall surface W5 of the recess comprise a curved surface, a force F applied from the outer wall surface W4 is spread over the entire wall surface W5 and does not become concentrated on a specific section, and therefore, it is possible to prevent damage to the recess of reinforcing member B due to that force. However, with the above-mentioned second conventional technology, there is a problem that it is not easy to keep the reinforcing member B stationary on a flat work bench, and the working efficiency of housing the coupling section of the optical fiber coupler within the recess is remarkably reduced (refer to FIG. 9).
In addition, with respect to flat-surface processing and curved-surface processing, the cost of curved-surface processing is high, and therefore, with the reinforcing member which uses the above-mentioned second conventional technology which has more curved surfaces, there is a tendency for manufacturing costs to be higher.
In addition, since in both of the above-mentioned first and second conventional technologies, both ends of the respective recesses have sharp edges, there is a possibility that the optical fiber will become damaged or cut by contact with those parts.
In addition, when the reinforcing member is a super invar material or an invar material, metal plating is carried out in order to supplement anti-corrosiveness, but it is impossible to obtain sufficient anti-corrosiveness to prevent rust from occurring on the reinforcing member, and as a result, rust occurs on the reinforcing member, and there is a possibility that the properties of the optical fiber coupler will change. In addition, in that case, since the surface of the reinforcing member is very smooth, the adhesive which is used to fix the coupling section L cannot obtain sufficient adhesive strength through the anchoring effect. For that reason, when an external force is applied to an optical fiber connected to the coupling section, there is a possibility that the adhered section will peel away and become damaged.
The place at which the optical fiber coupler is arranged is not limited to indoors and arrangement outside also occurs. In that situation, in addition to the above-mentioned reinforcing member, the optical fiber coupler is housed within an external unit having high light shielding properties and air tightness. As the external unit, a cylindrical member being superior in strength is used.